Method for transferring carbon nanotube array and method for forming carbon nanotube structure

ABSTRACT

A method for transferring a carbon nanotube array is provided. A substitute substrate, a growing substrate, and a carbon nanotube array grown on the growing substrate are provided. The carbon nanotube array has a bottom surface adjacent to the growing substrate and a top surface away from the growing substrate. The substitute substrate is placed on the top surface of the carbon nanotube array and PVA solution is sandwiched between the substitute substrate and the carbon nanotube array. The PVA solution is frozen between the substitute substrate and the carbon nanotube array. The substitute substrate is separated from the growing substrate to separate the bottom surface of the carbon nanotube array from the growing substrate. The solvent in the solid PVA solution is removed and only PVA is left between the substitute substrate and the carbon nanotube array. A method for forming a carbon nanotube structure is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201410272103.3, filed on Jun. 18, 2014 inthe China Intellectual Property Office, the contents of which are herebyincorporated by reference. This application is related to applicationsentitled, “METHOD FOR TRANSFERRING CARBON NANOTUBE ARRAY AND METHOD FORFORMING CARBON NANOTUBE STRUCTURE”, filed Jun. 20, 2014, Ser. No.14/310,301 and “METHOD FOR TRANSFERRING CARBON NANOTUBE ARRAY AND METHODFOR FORMING CARBON NANOTUBE STRUCTURE”, filed Jun. 20, 2014, Ser. No.14/310,295.

FIELD

The subject matter herein generally relates to methods for transferringcarbon nanotube arrays and methods for forming carbon nanotubestructures.

BACKGROUND

Carbon nanotube film can be fabricated by drawing from a carbon nanotubearray grown on a growing substrate (e.g., silicon wafer), as disclosedby U.S. Pat. No. 8,048,256 to Feng et al. The carbon nanotube film isfree standing and comprises a plurality of carbon nanotubes joinedend-to-end by van der Waals attractive force therebetween. The carbonnanotubes in the carbon nanotube film are substantially aligned alongthe lengthwise direction of the carbon nanotube film, and thus, thecarbon nanotube film has good thermal and electrical conductivity alongthe direction of the aligned carbon nanotubes. The carbon nanotube filmis substantially transparent and can be used as a conductive thin film.Therefore, the carbon nanotube film can be used in many differentfields, such as touch panels, liquid crystal displays, speakers, heatingdevices, thin film transistors, cables, and the like.

BRIEF DESCRIPTION OF THE DRAWING

Implementations of the present technology will now be described, by wayof example only, with reference to the attached figures, wherein:

FIG. 1 is a flow chart of an embodiment of a method for transferring acarbon nanotube array.

FIG. 2 is a schematic structural view of an embodiment of a method fortransferring a carbon nanotube array.

FIG. 3 shows a scanning electron microscope (SEM) image of a carbonnanotube film drawn from the carbon nanotube array.

FIG. 4 shows carbon nanotubes joined end-to-end.

FIG. 5 is a schematic structural view of another embodiment of themethod for transferring the carbon nanotube array.

FIG. 6 is a schematic structural view of yet another embodiment of themethod for transferring the carbon nanotube array.

FIG. 7 is a flow chart of an embodiment of a method for forming a carbonnanotube structure.

FIG. 8 is a schematic structural view of an embodiment of a method forforming a carbon nanotube structure.

FIG. 9 shows an optical photo of drawing the carbon nanotube film fromthe carbon nanotube array transferred to a substitute substrate.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “another,” “an,” or “one” embodiment in this disclosure are notnecessarily to the same embodiment, and such references mean “at leastone.”

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures and components have notbeen described in detail so as not to obscure the related relevantfeature being described. Also, the description is not to be consideredas limiting the scope of the embodiments described herein. The drawingsare not necessarily to scale and the proportions of certain parts havebeen exaggerated to better illustrate details and features of thepresent disclosure.

Several definitions that apply throughout this disclosure will now bepresented.

The term “contact” is defined as a direct and physical contact. The term“substantially” is defined to be essentially conforming to theparticular dimension, shape, or other description that is described,such that the component need not be exactly conforming to thedescription. The term “comprising,” when utilized, means “including, butnot necessarily limited to”; it specifically indicates open-endedinclusion or membership in the so-described combination, group, series,and the like.

Referring to FIG. 1 and FIG. 2, the present disclosure is described inrelation to a method for transferring a carbon nanotube array 10.

In block S1, a substitute substrate 30 and a growing substrate 20 areprovided. The growing substrate 20 has a carbon nanotube array 10 grownthereon, and the carbon nanotube array 10 is in a state that is capableof having the carbon nanotube structure 40 drawn therefrom. The carbonnanotube array 10 comprises a bottom surface 102 adjacent to the growingsubstrate 20 and a top surface 104 away from the growing substrate 20.

In block S2, the substitute substrate 30 is placed on the top surface104 of the carbon nanotube array 10, and a liquid medium 60 issandwiched between a surface of the substitute substrate 30 and the topsurface 104 of the carbon nanotube array 10. The liquid medium 60 is aliquid solution of polyvinyl alcohol (PVA). The PVA is dissolved in asolvent to form the liquid solution.

In block S3, the liquid medium 60 between the substitute substrate 30and the carbon nanotube array 10 is solidified into solid medium 60′.

In block S4, the substitute substrate 30 and the growing substrate 20are moved away from each other, thereby separating the carbon nanotubearray 10 from the growing substrate 20.

In block S5, after the carbon nanotube array 10 is transferred from thegrowing substrate 20 onto the substitute substrate 30, the solvent inthe solid medium 60′ between the substitute substrate 30 and the carbonnanotube array 10 is removed by heating. The state of the carbonnanotube array 10, before, during, and after the transfer onto thesubstitute substrate 30, and after the removal of the solid medium 60′,is still capable of having the carbon nanotube structure 40 drawntherefrom.

The carbon nanotube structure 40 can be a free-standing structureincluding a plurality of carbon nanotubes joined end-to-end by van derWaals attractive force therebetween. The carbon nanotube structure 40can be a carbon nanotube film or a carbon nanotube wire.

The carbon nanotube array 10 is grown on the growing substrate 20 by achemical vapor deposition (CVD) method. The carbon nanotube array 10comprises a plurality of carbon nanotubes oriented substantiallyperpendicular to a growing surface of the growing substrate 20. Thecarbon nanotubes in the carbon nanotube array 10 are closely bondedtogether side-by-side by van der Waals attractive forces. By controllinggrowing conditions, the carbon nanotube array 10 can be essentially freeof impurities such as carbonaceous or residual catalyst particles.Accordingly, the carbon nanotubes in the carbon nanotube array 10 areclosely contacting each other, and a relatively large van der Waalsattractive force exists between adjacent carbon nanotubes. The van derWaals attractive force is so large that when drawing a carbon nanotubesegment (e.g., a few carbon nanotubes arranged side-by-side), adjacentcarbon nanotube segments can be drawn out end-to-end from the carbonnanotube array 10 due to the van der Waals attractive forces between thecarbon nanotubes. The carbon nanotubes are continuously drawn to form afree-standing and macroscopic carbon nanotube structure 40, which can bein the shape of a film or a wire. The carbon nanotube array 10 that canhave the carbon nanotube structure 40 drawn therefrom can be a superaligned carbon nanotube array. A material of the growing substrate 20can be P-type silicon, N-type silicon, or other materials that aresuitable for growing the super aligned carbon nanotube array.

The carbon nanotube structure 40 drawn from the carbon nanotube array 10comprises a plurality of carbon nanotubes joined end-to-end and can be afree-standing carbon nanotube film. The carbon nanotube film comprises aplurality of carbon nanotubes substantially aligned along the samedirection.

Referring to FIG. 3 and FIG. 4, the carbon nanotube film can comprise orconsist of a plurality of carbon nanotubes. In the carbon nanotube film,the overall aligned direction of a majority of the carbon nanotubes issubstantially aligned along the same direction parallel to a surface ofthe carbon nanotube film. A majority of the carbon nanotubes aresubstantially aligned along the same direction in the carbon nanotubefilm. Along the aligned direction of the majority of carbon nanotubes,each carbon nanotube is joined to adjacent carbon nanotubes end to endby van der Waals attractive force therebetween, whereby the carbonnanotube film is capable of being free-standing structure. There may bea minority of carbon nanotubes in the carbon nanotube film that arerandomly aligned. However, the number of the randomly aligned carbonnanotubes is very small, in comparison, and does not affect the overalloriented alignment of the majority of carbon nanotubes in the carbonnanotube film. Some of the majority of the carbon nanotubes in thecarbon nanotube film that are substantially aligned along the samedirection may not be exactly straight, and can be curved at a certaindegree, or not exactly aligned along the overall aligned direction by acertain degree. Therefore, partial contacts can exist between thejuxtaposed carbon nanotubes in the majority of the carbon nanotubesaligned along the same direction in the carbon nanotube film. The carbonnanotube film can comprise a plurality of successive and oriented carbonnanotube segments. The plurality of carbon nanotube segments are joinedend to end by van der Waals attractive force. Each carbon nanotubesegment comprises a plurality of carbon nanotubes substantially parallelto each other, and the plurality of paralleled carbon nanotubes are incontact with each other and combined by van der Waals attractive forcetherebetween. The carbon nanotube segment has a desired length,thickness, uniformity, and shape. There can be clearances betweenadjacent and juxtaposed carbon nanotubes in the carbon nanotube film. Athickness of the carbon nanotube film at the thickest location is about0.5 nanometers to about 100 microns (e.g., in a range from 0.5nanometers to about 10 microns). When the carbon nanotube structure 40has a small width, the carbon nanotube structure 40 can be afree-standing carbon nanotube wire.

The term “free-standing” comprises, but is not limited to, a structurethat does not need to be supported by a substrate. For example, afree-standing carbon nanotube structure 40 can sustain the weight ofitself when it is hoisted by a portion thereof without any significantdamage to its structural integrity. If the free-standing carbon nanotubestructure 40 is placed between two separate supporters, a portion of thefree-standing carbon nanotube structure 40 suspended between the twosupporters can maintain structural integrity. The free-standing carbonnanotube structure 40 can be realized by the successive carbon nanotubesjoined end to end by van der Waals attractive force.

In the present disclosure, the growing of the carbon nanotube array 10and the drawing of the carbon nanotube structure 40 are processed ondifferent structures (i.e., the growing substrate 20 and the substitutesubstrate 30). The substitute substrate 30 for drawing the carbonnanotube structure 40 can be made of low-price materials, and thegrowing substrate 20 can be recycled quickly. Thus, production of thecarbon nanotube structure 40 can be optimized.

The substitute substrate 30 can be a soft, elastic, or rigid solidsubstrate. The substitute substrate 30 has a surface to accept thecarbon nanotube array 10 thereon. The surface of the substitutesubstrate 30 can be flat when the carbon nanotube array 10 is grown on aflat growing surface of the growing substrate 20. During transferring ofthe carbon nanotube array 10 from the growing substrate 20 to thesubstitute substrate 30, the state of the carbon nanotube array 10 isstill capable of drawing the carbon nanotube structure 40 from thecarbon nanotube array 10 on the substitute substrate 30. The carbonnanotube array 10 transferred to the substitute substrate 30 is still asuper aligned carbon nanotube array. The carbon nanotubes of the carbonnanotube array 10 are substantially perpendicular to the surface of thesubstitute substrate 30.

The carbon nanotube array 10 is arranged upside down on the surface ofthe substitute substrate 30. The carbon nanotubes are grown from thegrowing surface of the growing substrate 20 to form the carbon nanotubearray 10. The carbon nanotube comprises a bottom end adjacent orcontacting the growing substrate 20 and a top end away from the growingsubstrate 20. The bottom ends of the carbon nanotubes form the bottomsurface 102 of the carbon nanotube array 10, and the top ends of thecarbon nanotubes form the top surface 104 of the carbon nanotube array10. After the carbon nanotube array 10 is transferred to the substitutesubstrate 30, the top surface 104 of the carbon nanotube array 10 is nowadjacent to or contacting the substitute substrate 30, and the bottomsurface 102 of the carbon nanotube array 10 is now away from thesubstitute substrate 30.

In block S2, the liquid medium 60 can be in a shape of fine droplets,mist, or film. The liquid medium 60 can spread on the entire top surface104. The solvent of the liquid medium 60 can be water and/or organicsolvents with small molecular weights that are volatile at roomtemperature or easily evaporated by heating. The solvent can dissolvethe PVA. The amount of the PVA in the liquid medium 60 can be as smallas possible. In one embodiment, the weight percentage of the PVA in theliquid solution and the liquid medium 60 is about 0.1% to about 2%. Theorganic solvent can be selected from ethanol, methanol, and acetone. Theliquid medium 60 can have a poor wettability for carbon nanotubes. Thus,when a small amount of liquid medium 60 is on the top surface 104 of thecarbon nanotube array 10, it cannot infiltrate inside the carbonnanotube array 10 and will not affect the state of the carbon nanotubearray 10. A diameter of the liquid medium droplet and a thickness of theliquid medium film can be in a range from about 10 nanometers to about300 microns. The substitute substrate 30 and the top surface 104 of thecarbon nanotube array 10 are both in contact with the liquid medium 60.

In block S2, to maintain the state of the carbon nanotube array 10 ofbeing capable of drawing the carbon nanotube structure 40, thesubstitute substrate 30 may apply a pressing force as small as possibleto the carbon nanotube array 10. The pressing force can satisfy0<f<2N/cm². The pressing force does not press the carbon nanotubes downor vary the length direction of the carbon nanotubes in the carbonnanotube array 10. The carbon nanotubes in the carbon nanotube array 10between the substitute substrate 30 and the growing substrate 20 arealways substantially perpendicular to the growing surface of the growingsubstrate 20.

In one embodiment, block S2 comprises blocks S21 and S22.

In block S21, the liquid medium 60 is formed on the top surface 104 ofthe carbon nanotube array 10. The liquid medium 60 can be formed intofine droplets or a mist in the air and drop or collect onto the topsurface 104 of the carbon nanotube array 10.

In block S22, the substitute substrate 30 and the carbon nanotube array10 on the growing substrate 20 are brought together such that thesurface of the substitute substrate 30 and the liquid medium 60 on thetop surface 104 are contacting each other.

In another embodiment, block S2 comprises blocks S21′ and S22′.

In block S21′, the liquid medium 60 is formed on the surface of thesubstitute substrate 30. The liquid medium 60 can be formed into finedroplets or a mist in the air and drop or collect onto the surface ofthe substitute substrate 30.

In block S22′, the substitute substrate 30 and the carbon nanotube array10 on the growing substrate 20 are brought together such that the topsurface 104 of the carbon nanotube array 10 and the liquid medium 60 onthe surface of the substitute substrate 30 are contacting each other.

In block S3, the temperature of the liquid medium 60 can be decreased tobe below the freezing point of the liquid medium 60. For example, whenusing water as the solvent, the liquid medium 60 is frozen below 0° C.After the liquid medium 60 is solidified, the substitute substrate 30and the carbon nanotube array 10 can be firmly bonded together by thesolid medium 60′ therebetween.

Referring to FIG. 5, in one embodiment, the laminate of the growingsubstrate 20, the carbon nanotube array 10, the liquid medium 60, andthe substitute substrate 30 can be put into a freezer 70 with atemperature below the freezing point to freeze the liquid medium 60.

Referring to FIG. 6, in another embodiment, when block S2 comprisesblocks S21 and S22, a temperature of the substitute substrate 30 can bedecreased to below the freezing point before block S22. For example,before block S22, the substitute substrate 30 can be kept in the freezer70 for a period of time until the substitute substrate 30 reaches atemperature below the freezing point. Thus, when the substitutesubstrate 30 contacts the liquid medium 60 on the top surface 104 of thecarbon nanotube array 10, the liquid medium 60 can be directly frozeninto solid medium 60′.

In block S4, due to the bonding between the carbon nanotube array 10 andthe substitute substrate 30 by the solid medium 60′, the separating ofthe two substrates can separate the carbon nanotube array 10 from thegrowing substrate 20. During the separating, a majority of the carbonnanotubes in the carbon nanotube array 10 can be detached from thegrowing substrate 20 at the same time by cutting means, or moving eitherthe substitute substrate 30 or the growing substrate 20, or both, awayfrom each other along a direction substantially perpendicular to thegrowing surface of the growing substrate 20. The carbon nanotubes of thecarbon nanotube array 10 are detached from the growing substrate 20along the growing direction of the carbon nanotubes. When both thesubstitute substrate 30 and the growing substrate 20 separate, the twosubstrates both moves along the direction perpendicular to the growingsurface of the growing substrate 20 and depart from each other.

In block S5, the heating can melt the solid medium 60′ into liquidmedium and dry the solvent in the liquid medium between the substitutesubstrate 30 and the carbon nanotube array 10. In another embodiment,the heating can directly sublimate the solvent in the solid medium 60′.The heating removes the solvent and leaves the PVA between the carbonnanotube array 10 and the substitute substrate 30. The removal of thesolvent does not affect the state of the carbon nanotube array 10. Dueto the amount of the PVA in the liquid and solid medium 60, 60′ is verysmall, after the removal of the solvent, the substitute substrate 30 andthe top surface 104 of the carbon nanotube array 10 are mainly bonded byvan der Waals attractive forces. Meanwhile, the PVA also provides aforce to the substitute substrate 30 and the top surface 104 of thecarbon nanotube array 10 to provide a stable bonding. However, theexistence of PVA does not affect the drawing of the carbon nanotubestructure 40 from the carbon nanotube array 10.

For drawing the carbon nanotube structure 40, the bonding force betweenthe carbon nanotube array 10 and the substitute substrate 30 should besmall to continuously draw carbon nanotubes out from the carbon nanotubearray 10. In blocks S3 to S5, the bonding force is increased by theforming of the solid medium 60′ to separate the carbon nanotube array 10from the growing substrate 20 and decreased by removing the solvent inthe solid medium 60′ before drawing the carbon nanotube structure 40.Thus, the material of the substitute substrate 30 is not limited and canbe at least one of metal, glass, crystal, ceramic, silicon, silicondioxide, plastic, and resin, such as polymethyl methacrylate andpolyethylene terephthalate.

It is to be noted that using pure solvent as the liquid medium 60 canalso provide an enough bonding force for the separating of the carbonnanotube array 10 from the growing substrate 20 due to the solidifyingof the liquid medium 60. However, in this situation, after removing thesolvent, the carbon nanotube array 10 and the substitute substrate 30are combined all by the van der Waals attractive force therebetween. Andthis may not be enough for the drawing of the carbon nanotube structure40, because if the bonding force between the carbon nanotube array 10and the substitute substrate 30 is too small, the entire carbon nanotubearray 10 may be drawn away from the substitute substrate 30 at one time.By using the PVA, after removing the solvent, the carbon nanotube array10 and the substitute substrate 30 are combined not only by the van derWaals attractive force therebetween but also by the PVA. Therefore, thebinding force can be not too large and not too small. In someembodiments, the weight percentage of the PVA in the liquid solution andthe liquid medium 60 is equal to or smaller than 2%.

Referring to FIG. 6 and FIG. 7, the present disclosure is described inrelation to a method for forming a carbon nanotube structure 40including the previously described blocks S1 to S5, and furtherincluding block S6. In block S6, the carbon nanotube structure 40 isdrawn from the carbon nanotube array 10 on the substitute substrate 30.

Referring to FIG. 8, in the block S6, the carbon nanotube structure 40is drawn from the carbon nanotube array 10 that was transferred to thesubstitute substrate 30, not from the carbon nanotube array 10 locatedon the growing substrate 20. In one embodiment of block S6, the carbonnanotube structure 40 can be drawn from the carbon nanotube array 10upside down on the surface of the substitute substrate 30 (i.e., drawnfrom the bottom surface 102 of the carbon nanotube array 10).

Block S6 can comprise block S61 and S62:

In block S61, a carbon nanotube segment having a predetermined width isdrawn from the carbon nanotube array 10 on the substitute substrate 30.The segment is selected using a drawing tool 50 (e.g., adhesive tape,pliers, tweezers, or other tool allowing multiple carbon nanotubes to begripped and pulled simultaneously).

In block S62, a plurality of carbon nanotube segments joined end to endby van der Waals attractive force is drawn by moving the drawing tool50, thereby forming a continuous carbon nanotube structure 40.

In block S61, the carbon nanotube segment comprises a single carbonnanotube or a plurality of carbon nanotubes substantially parallel toeach other. The drawing tool 50 such as adhesive tape can be used forselecting and drawing the carbon nanotube segment. The adhesive tape maycontact with the carbon nanotubes in the carbon nanotube array to selectthe carbon nanotube segment. The drawing tool 50 can select a largewidth of carbon nanotube segments to form the carbon nanotube film, or asmall width of the carbon nanotube segments to form the carbon nanotubewire.

In block S62, an angle between a drawing direction of the carbonnanotube segments and the growing direction of the carbon nanotubes inthe carbon nanotube array 10 can be larger than 0 degrees (e.g., 30° to90°).

Block S4 is different from block S6. The purpose of block S4 is toseparate the carbon nanotube array 10 as a whole from the growingsubstrate 20. The carbon nanotube array 10 separated from the growingsubstrate 20 still in the array shape. The purpose of block S6 is todraw out carbon nanotubes one by one or segment by segment to form acarbon nanotube film or wire from the carbon nanotube array 10 on thesubstitute substrate 30.

In the present method for making the carbon nanotube structure 40, thegrowing of the carbon nanotube array 10 and the drawing of the carbonnanotube structure 40 can be processed on different substrates. Thesubstitute substrate 30 can be made of cheap material, and the expensivegrowing substrate 20 can be recycled quickly and used again for growingnew carbon nanotube arrays 10, thus speeding up the production of thecarbon nanotube arrays.

Depending on the embodiment, certain blocks/steps of the methodsdescribed may be removed, others may be added, and the sequence ofblocks may be altered. It is also to be understood that the descriptionand the claims drawn to a method may comprise some indication inreference to certain blocks/steps. However, the indication used is onlyto be viewed for identification purposes and not as a suggestion as toan order for the blocks/steps.

The embodiments shown and described above are only examples. Even thoughnumerous characteristics and advantages of the present technology havebeen set forth in the foregoing description, together with details ofthe structure and function of the present disclosure, the disclosure isillustrative only, and changes may be made in the detail, especially inmatters of shape, size and arrangement of the parts within theprinciples of the present disclosure up to, and including the fullextent established by the broad general meaning of the terms used in theclaims. It will therefore be appreciated that the embodiments describedabove may be modified within the scope of the claims.

What is claimed is:
 1. A method for transferring a carbon nanotubearray, the method comprising: providing a substitute substrate, agrowing substrate, and a carbon nanotube array grown on the growingsubstrate; the carbon nanotube array comprises a bottom surface adjacentto the growing substrate and a top surface away from the growingsubstrate; and the carbon nanotube array comprises an ability to have acarbon nanotube structure drawn therefrom; placing the substitutesubstrate on the top surface of the carbon nanotube array andsandwiching a liquid solution of polyvinyl alcohol between thesubstitute substrate and the carbon nanotube array, and the liquidsolution of polyvinyl alcohol comprising polyvinyl alcohol dissolved ina solvent; solidifying the liquid solution of polyvinyl alcohol betweenthe substitute substrate and the carbon nanotube array into solidmedium; separating the substitute substrate from the growing substrate,thereby separating the bottom surface of the carbon nanotube array fromthe growing substrate; and removing the solvent in the solid medium andleaving the polyvinyl alcohol between the substitute substrate and thecarbon nanotube array, and the carbon nanotube array still having theability to have a carbon nanotube structure drawn therefrom.
 2. Themethod of claim 1, wherein the carbon nanotube structure is a carbonnanotube film or a carbon nanotube wire.
 3. The method of claim 1,wherein the carbon nanotube structure comprises a plurality of carbonnanotubes joined end to end.
 4. The method of claim 1, wherein theliquid solution of polyvinyl alcohol is in a shape of a plurality ofdroplets, mist, or film.
 5. The method of claim 4, wherein a diameter ofthe droplets and a thickness of the film is in a range from about 10nanometers to about 300 microns.
 6. The method of claim 1, wherein thesandwiching the liquid solution of polyvinyl alcohol between thesubstitute substrate and the carbon nanotube array comprises: formingthe liquid solution of polyvinyl alcohol on the top surface of thecarbon nanotube array; and contacting a surface of the substitutesubstrate and the liquid solution of polyvinyl alcohol on the topsurface with each other.
 7. The method of claim 6, wherein thesolidifying the liquid solution of polyvinyl alcohol between thesubstitute substrate and the carbon nanotube array comprises contactingthe substitute substrate, having a temperature below a freezing pointwith the liquid solution of polyvinyl alcohol, on the top surface of thecarbon nanotube array.
 8. The method of claim 1, wherein the sandwichingthe liquid solution of polyvinyl alcohol between the substitutesubstrate and the carbon nanotube array comprises: forming the liquidsolution of polyvinyl alcohol on a surface of the substitute substrate;and contacting the top surface of the carbon nanotube array and theliquid solution of PVA polyvinyl alcohol on the surface of thesubstitute substrate with each other.
 9. The method of claim 8, whereinthe solidifying the liquid solution of polyvinyl alcohol between thesubstitute substrate and the carbon nanotube array comprises exposing alamination of the growing substrate, the carbon nanotube array, theliquid solution of polyvinyl alcohol, and the substitute substrate to anenvironment having an internal temperature below a freezing point of thesolvent in the liquid solution of polyvinyl alcohol.
 10. The method ofclaim 1, wherein a weight percentage of the liquid solution of polyvinylalcohol is equal to or smaller than 2%.
 11. The method of claim 1,wherein a weight percentage of the liquid solution of polyvinyl alcoholis from about 0.1% to about 2%.
 12. The method of claim 1, wherein thecarbon nanotube array comprises a plurality of carbon nanotubes, andduring the separating the carbon nanotube array from the growingsubstrate, substantially all carbon nanotubes are simultaneouslydetached from the growing substrate.
 13. The method of claim 1, whereinthe carbon nanotube array comprises a plurality of carbon nanotubes, andthe plurality of carbon nanotubes of the carbon nanotube array aredetached from the growing substrate along a growing direction of theplurality of carbon nanotubes.
 14. The method of claim 1, wherein thegrowing substrate comprises a growing surface for growing the carbonnanotube array, and a moving direction of at least one of the substitutesubstrate and the growing substrate is substantially perpendicular tothe growing surface of the growing substrate during the separating ofthe at least one of the substitute substrate and the growing substrate.15. A method for transferring a carbon nanotube array, the methodcomprising: providing a first substrate, a second substrate, and acarbon nanotube array grown on the first substrate, the carbon nanotubearray having a bottom surface adjacent to the first substrate and a topsurface away from the first substrate, and the carbon nanotube arrayhaving an ability to have a carbon nanotube structure drawn therefrom;placing the second substrate on the top surface of the carbon nanotubearray and sandwiching a liquid solution of polyvinyl alcohol between thesecond substrate and the carbon nanotube array, and the liquid solutionof polyvinyl alcohol comprising polyvinyl alcohol dissolved in asolvent; solidifying the liquid solution of polyvinyl alcohol betweenthe second substrate and the carbon nanotube array into a solid medium;separating the second substrate from the first substrate, therebyseparating the bottom surface of the carbon nanotube array from thefirst substrate; and removing the solvent in the solid medium andleaving the polyvinyl alcohol between the second substrate and thecarbon nanotube array, and the carbon nanotube array still having theability to have a carbon nanotube structure drawn therefrom.
 16. Amethod for forming a carbon nanotube structure, the method comprising:providing a substitute substrate, a growing substrate, and a carbonnanotube array grown on the growing substrate, the carbon nanotube arrayhaving a bottom surface adjacent to the growing substrate and a topsurface away from the growing substrate, and the carbon nanotube arrayhaving an ability to have a carbon nanotube structure drawn therefrom;placing the substitute substrate on the top surface of the carbonnanotube array and sandwiching a liquid solution of polyvinyl alcoholbetween the substitute substrate and the carbon nanotube array, and theliquid solution of polyvinyl alcohol comprising polyvinyl alcoholdissolved in a solvent; solidifying the liquid solution of polyvinylalcohol between the substitute substrate and the carbon nanotube arrayinto a solid medium; separating the substitute substrate from thegrowing substrate, thereby separating the bottom surface of the carbonnanotube array from the growing substrate; removing the solvent in thesolid medium and leaving the polyvinyl alcohol between the substitutesubstrate and the carbon nanotube array, and the carbon nanotube arraystill having the ability to have a carbon nanotube structure drawntherefrom; and drawing a plurality of carbon nanotube segments joinedend to end by van der Waals attractive force from the carbon nanotubearray transferred to the substitute substrate.